1. Field of the Invention
The present invention relates to a system for controling the moisture content in the subsurface soil to depths of 20 feet surrounding the foundation of a house or other building structure.
2. Prior Art
The prior art teaches the desirability of attempting to control the moisture content in the surface soil primarily for the purpose of irrigating plant life. However, none of the prior art teaches how to control the moisture content in the earth at subsoil depths up to 20 feet deep surrounding a house or other building structure in order to prevent damage to the foundation as described in the manner herein.
A preliminary patent search was conducted related to the present invention and the following patents were uncovered in the search:
______________________________________ Inventor U.S. Pat. No Date ______________________________________ Babin 2,798,768 July 9, 1957 Thomas 3,552,654 January 5, 1971 Cobb et al. 3,744,256 July 10, 1973 Fitzhugh 3,797,738 March 19, 1974 Chevreliere 3,905,551 September 16, 1975 Green 3,946,762 March 30, 1976 Maclay 3,991,939 November 16, 1976 Neal 4,197,866 April 15, 1980 ______________________________________
Babin U.S. Pat. No. 2,798,768 shows a pipe construction through which liquids can be pumped or flow freely while at the same time allowing small quantities of liquid to be discharged along the length of the pipe. The pipe construction of Babin may be positioned above ground, on the ground, or beneath the ground. This patent is directed to the irrigation of plant life.
Thomas U.S. Pat. No. 3,552,654 shows irrigation or soaking conduits composed of an outer skin which is substantially impervious to water and which is prepared with score lines thereby destroying the water-impervious nature and thus permitting water to seep from the conduit and irrigate or soak plant life in the soil.
Cobb et al. U.S. Pat. No. 3,744,256 shows an irrigation system which provides a continuous supply of fluid from a supply reservoir through a ring system or by gravity flow with varying degrees of porosity in a sealed-end system. This system is not pressurized or monitored with any type of metering device thereby providing unbalanced, continuous irrigation at all times with no shut-off controls.
Fitzhugh U.S. Pat. No. 3,797,738 shows a method for sub-surface drip soil irrigation of arid areas of land of varying sizes by providing wick manifolds which would randomly distribute water on a continuous basis regardless of the terrain or land leveling procedures.
Ayme de la Chevreliere U.S. Pat. No. 3,905,551 shows an automatic, above-ground sprinkling control mechanism which provides water to the earth after being signaled to do so by upper and lower placed, in-ground, soil electrodes.
Green U.S. Pat. No. 3,946,762 shows an irrigation or drainage system comprising one or more conduits having a mesh fabric sheath covering radially spaced apertures which, due to capillary action, permit uniform fluid distribution throughout the length of the sheath and the peripheral surrounding area
Maclay U.S. Pat. No. 3,991,939 shows an automated above-ground misting and cooling sprinkler system for use with ornamental and food-producing plants, shrubs, and crops not only to irrigate leaves and roots, but also to provide protection against damage to leaves by insects and heat.
Neal U.S. Pat. No. 4,197,866 shows a soil moisture sampler and control mechanism which automatically activates in-ground probes which measure moisture and, when less than a pre-set value, signal an irrigation timer to activate thus irrigating the soil for a preselected time interval. This system discloses a somewhat complicated electronic control circuit which is employed principally in the irrigation of fields and orchards.
The present invention relates to a system for a controlled distribution of water for the purpose of moistening the soil surrounding the foundation of a house or other building structure down to twenty feet and is directed to solving the problem of water distribution in such soil. The shrinking or swelling of subsurface soil has inflicted billions of dollars in damage to houses and buildings each year and has presented a monumental problem to owners who are directly affected. Because of these problems much work has gone into the development of a moisture distribution system which will specifically irrigate the earth surrounding a house or other building structure.
The present invention has been developed to specifically control the behavior and degree of moisture below ground. Subsurface water can be divided into two general classifications: the aeration zone and the saturation zone. The latter, more commonly termed the "water table," is the deepest level. The aeration zone includes a capillary fringe area which obtains moisture from the water table, an intermediate belt which contains moisture in dead storage such as one might find after a good rainstorm, and at the surface, the soil water belt which provides moisture for vegetable and plant roots.
Unless the soil water belt can replace capillary water usually provided by surface watering or rain showers, the soil will eventually dessicate through the effects of gravity, transpiration, and evaporation. In so doing, capillary water is lost--a critical factor which influences building foundations and their stability. Since the water content of the surface soil tends to remain relatively stable below very shallow depths, and since the availability of soil water derived from a water table ceases when the boundary lies at a depth exceeding the limit of capillary rise for a particular type soil, (from six inches to depths approaching twenty feet), it is the soil water belt and the uppermost portion of the intermediate belt which receive benefits from this invention.
Factors influencing foundation stability include: (1) soil content, (2) the moisture zone, and (3) vegetation present. Soil content can be coarse, i.e. gravels and sands, or fine, i.e. silts and clays. However, what accounts for more economic damage to structures than any other thing is the problem arising from the moisture content in partially saturated soils regardless of composition because only partially saturated soils can swell or shrink. Therefore, only water which penetrates these soils is of particular concern with respect to foundation stability. Variations in moisture within these expansive soils cause most foundation failures. These soils swell when wet causing upheaval and shrink when dry causing settlement. Any volumetric changes in the soil bearing the weight of the foundation causes differential foundation movement.
All types of soils can cause problems, but one type seems to be the most common offender--clay. Clay soils, which have a greater tendency for runoff as opposed to infiltration than do sandy soils, can be expansive when three conditions are met: (1) the soil contains the type of clay mineral subject to high volume change with increased moisture change; (2) the soil has been in a dessicated condition for at least part of the seasonal cycle; and (3) the strata containing the expansive clay mineral must be sufficiently thick to create significant movement.
The invention herein described would provide moisture to the soil water belt, the zone which affects foundation behavior the most and the intermediate belt which supports the aforementioned. The system would make available constant moisture which is necessary for foundation safety. The water table would have little, if any significant influence on soil moisture since all soils have an equilibrium moisture content dictated by gravity acting against forces holding water in the soil. This equilibrium would change in the upper or aeration zone because water is removed by one or a combination of three processes: transpiration (removal by vegetation), evaporation (removal into the air), and gravity (removal by a downward pull).
Loss of soil moisture beneath a foundation caused by evaporation would show the greatest effects closer to the surface. In exposed soil, evaporation forces are everpresent as long as atmospheric humidity is less than 100 percent. Clay soil under the confines of a slab foundation can be readily saturated by water injections; however, a natural tendency persists for moisture to migrate laterally as well as distally thereby escaping at the periphery. The installation of a vertical water barrier around a foundation perimeter would retard this natural water loss although it must be realized that the loss cannot be completely stopped. However, in the upper strata, a fluctuating condition can arise due to seasonal effects and to the forces of gravity whether the soil is covered or exposed. Therefore, construction design, i.e. slab versus crawl space, is not a critical factor because moisture content below a slab foundation tends to be higher than in surrounding exposed areas.